The present invention relates to a copolymerized polyamide and production process thereof. Particularly it relates to a high quality copolymerized polyamide excellent in moldability, heat resistance, chemicals resistance, etc. and a production process thereof.
Polyamides are widely used in the automobile industry and the electric and electronics industry as engineering plastics because of their excellent properties.
Conventionally used polyamides are mainly nylon 6 and nylon 66. In recent years, automobile engines have become higher in output and automobile engine rooms are packed more densely, which raises the atmospheric temperature, while the microelectronics industry has progressed to achieve smaller sizes and higher integration. In these situations, very thinly molded products which can withstand the use in a high temperature atmosphere are being demanded. However, nylon 6 and nylon 66 are respectively 220.degree. C. and 260.degree. C. in melting point (Tm), and even if they are reinforced by glass fibers, their critical heat distortion temperatures are the respective melting points.
Recently, as polyamide resin compositions which can withstand the use in a high temperature atmosphere, many compositions such as terephthalic acid-containing polyamide resins and their compositions, and their glass fiber-reinforced compositions were proposed (JP59-161428A, JP59-155426A, JP59-53536A, JP62-156130A, etc.). However, the polyamides containing terephthalic acid have had problems in moldability and coloring and been unsatisfactory in mechanical properties such as elongation, tensile strength, flexural strength and flexural modulus, and also in thermal deformability. Furthermore the production processes themselves are also liable to cause troubles. To solve these problems, various processes are proposed for polymerization to prepare polyamides.
From the viewpoint of decreasing heat history, the following polymerization processes are proposed: JP60-206827A proposes continuous polymerization at high temperature and high pressure in a short time, and JP2-41318A proposes continuous polymerization in a short time using a special apparatus. However, in these processes, changing specifics of the different kinds of products is complicated and ineffective. It has therefore demanded to develop a generally acceptable polymerization process. Change of articles is easy in batch polymerization, and there are several studies.
JP5-170895A and JP5-9381A propose to obtain a polyamide after forming a primary condensation product low in polymerization degree at a high pressure and at 250.degree. C. As stated in JP5-170895, batch polymerization has a problem that precipitation as a solid phase is caused in a polymerization reactor, and to prevent it, it has been necessary to polymerize at a low temperature of lower than 250.degree. C. or to polymerize at a high pressure of 23 kg/cm2-G or more. The primary condensation product thus obtained is low in relative viscosity, and when the polymerization degree is raised, enormous heat degrades the polymer color tone, crystallinity and melt stability, not allowing a polyamide with good quality to be obtained. For raising the polymerization degree, it is proposed to effect long-time solid-phase polymerization (JP2-41318) and to use an extruder for raising the polymerization degree in a molten state at high temperature (JP3-43417A, JP3-17156A, JP59-155433A, and JP5-43681A).
The solid-phase polymerization for raising the polymerization degree has a problem that it takes a very long time. On the other hand, raising the polymerization degree in a molten state requires a high temperature and is liable to cause thermal degradation, hence such problems as poorer color tone, lower mechanical strength and lower moldability. JP3-43417 uses tetrakis(2,4-di-t-butylphenyl)-4,4'-bisphenylene phosphonite as a heat resistant stabilizer for raising the polymerization degree. However, since the reaction is effected at 340.degree. to 345.degree.C., the improvement of heat history is insufficient. In view of this prior art, the present invention as described later has been completed. JP3-17156A and JP59-155433A use an extruder for raising the polymerization degree in continuous polymerization, but except the description "designed to let out from the degassing vent" at the time of extrusion, there is no method described for decreasing the heat history due to screw arrangement and forced degassing. JP5-43681A uses a phosphoric acid based compound as a catalyst for raising the polymerization degree, to raise the polymerization rate, but since a vent opened in atmosphere is used, no essential solving measure for degassing of condensed water, etc. is taken. Furthermore, the residence time of reaction is so long as to cause thermal degradation, and the product obtained is not satisfactory in properties.
In these copolymerized polyamides, the relationships between the distribution of respectively adjacent amide bonds and crystallization behavior on one hand and the intended properties on the other hand have not been known.